Filament connection for electric lamp or similar device



March 29, 1966, s. c. ACKERMAN FILAMENT CONNECTION FOR ELECTRIC LAMP 0RSIMILAR DEVICE Filed Feb. 5, 1964 United States Patent York Filed Feb.3, 1964, Ser. No. 341,859 6 Claims. (Cl. 313271) This invention relatesin general to electric incandescent lamps and similar devices and moreparticularly to an improved joint or connection between the filament andleading-in conductors of such devices.

In the service for which certain types of incandescent lamps areintended, the lamp is normally subjected to constant or prolongedperiods of severe high-frequency vibration. This is particularly true,for instance, in the case of lamps employed for aircraft service such asaircraft landing lamps. Where the filaments of such lamps are, forreasons of improved lamp efficiency, unsupported except for their pointsof connection to the customarily larger diameter and stiffer lead-inconductors or wires of the lamp, the resulting flexure of the filamentproduced by the vibration of the lamp subjects the filament connectionsor joints to severe stresses such as would ordinarily cause the earlyfailure thereof if the filament strength at and adjacent the connectionis insufficient. Adequate filament or mount strength against suchvibration and resulting stresses therefore becomes an important factorin the construction of such type lamps.

For the purpose of strengthening the filament joints in suchhigh-vibration service lamps, and also increasing the current-carryingcapacity of the filament wire at and near the usual welded connectionthereof to the lead-in conductors or wires, it has been customary toprovide a wire slip-over coil on each of the end legs of the filament.However, despite the presence of such a slip-over coil, there still is asudden change in the flexibility of the filament at the points ofconnection thereof to the leadin conductors or wires. As a result, whenthe filament is subjected to vibration, the stresses produced thereinare localized at, and are greatest at the said points of abruptflexibility change in the filament, with the result that thefilamentsoon becomes broken at one or the other of such points.Accordingly, filament connections such as described are of relativelylow strength and inadequate resistance to Withstand stresses such as arecustomarily imposed on the connections by the vibration normallyencountered in aircraft service.

It is an object of my invention, therefore to provide an electricincandescent lamp or similar device with a filament joint of greatlyimproved strength and resistance to vibrational stresses.

Another object of my invention is to provide an electric incandescentlamp or similar device with a filament joint of a construction such asto produce a gradual decrease in the flexibility of the filament fromits main body portion to its points of fixed attachment to the lead-inconductors.

Still another object of my invention is to provide an electricincandescent lamp or similar device with a fila- ,ment having either astraight wire or a coiled end leg joined to a rigid lead-in conductor bya connection producing a gradually decreasing flexibility gradient 'inthe filament from its main body portion outwardly thereof to a point ofrigid attachment of the filament end leg to the lead-in conductor, andin addition producing a dampening action on the vibration resonancefrequency of the filament.

Briefly stated, in accordance with one aspect of the invention, thestraight Wire or coiled end legs of the filament which are rigidlyattached to the lead-in conductors of the lamp are provided with Wireslip-over coils of progressively and substantially uniformly increasingstiffness outwardly toward the respective lead-in conductor. To suchend, the wire slip-over coils are, in accordance with a preferred formof the invention, formed of progressively and uniformly increasing coilpitch in a direction outwardly toward the respective lead-in conductor.

Further objects and advantages of the invention will appear from thefollowing detailed description of species thereof and from theaccompanying drawing.

In the drawing, FIG. 1 isan elevation, in section, of an electricincandescent lamp having a filament joint comprising my invention.

FIG. 2 is a perspective view, on an enlarged scale, of the mountstructure of the lamp shown in FIG. 1.

FIG. 3 is a transverse section, on a greatly enlarged scale, of themount structure and showing one of the filament joints thereof insection, and

FIG. 4 is an elevation, partly in section and on a greatly enlargedscale, of a modified form of filament joint comprising my invention.

Referring to the drawing, the invention is there illustrated as embodiedin an electric incandescent lamp of the self-contained reflector typesuch as described and claimed in US. Patent 2,148,314, Wright, issuedFebruary 21, 1939, and assigned to the assignee of the presentinvention. The lamp comprises a 'bulb or envelope 1 consisting of apreformed pressed glass reflector section 2 sealed around its peripheryto a preformed pressed glass cover section 3. The interior surface ofthe reflector section 2 is of suitable light-concentrating shape such asparaboloidal for instance, and it is covered with a metallic coating 4,preferably of aluminum, to constitute a reflecting surface. Mounted onthe reflector section 2, exteriorly thereof and at the apexofsaidsection, is a base structure 5. The base structure 5 may be of the typedescribed and claimed in US. Patent 2,272,512, Cotman et al., datedFebruary 10, 1942, and comprising a pair of metal lugs 6 suitablysecured, as by soldering, to metallic cups or thimbles 7 havingfeathered edges sunk and embedded in the glass of the reflector section2 around openings 8 therein, the cups or thimbles 7 thus hermeticallyclosing the said openings 8. The envelope 1 is exhausted and filled witha suitable inert gas through an exhaust tube 9 attached to the reflectorsection 2 at its apex. After the gas filling is introduced into the lampenvelope, the exhaust tube 9 is tipped off, as indicated at 10, tohermetically seal the envelope.

Mounted within the envelope 1 and supported therein from the metalthimbles 7 is a mount structure 11 comprising an electric energytranslation element or filament 12 disposed between and connected to apair of rigid leadin wires or conductors 13 of suitable material, suchas nickel or iron. The lead-in conductors 13 are rigidly secured attheir outer ends to the metal thimbles 7, as by being soldered or brazedtherewithin, and they extend straight through the respective openings 8in the reflector section into the interior of, and in more or lessparallel relation to one another and preferably in a plane parallel toand including the axis of the reflector section 2. The lead-inconductors 13 are held in rigid spaced relation by an insulating bridgeor cross bar member comprising a glass rod 14 extending between andsecured to the lead-in conductors 13 by short fastening wires 15 whichmay be spot-welded to the lead-in conductors.

The filament 12 is constituted of tungsten or other suitable refractorymetal wire and, in the particular case illustrated, comprises a linearcoiled-coil or main body portion 16 disposed coaxially of the reflectoraxis in a position in definite optical relation'to the" focus of thereflecting surface 4, preferably symmetrically about the Patented Mar.29, 1966 reflector focus. Each end of the filament 12 is provided withan end section or leg portion extending laterally across and rigidlyconnected to the respective lead-in conductor 13. In the form of theinvention shown in FIGS. 1 to 3, the filament end legs are comprised ofstraight or uncoiled w'iresections17 while in the modified form of theinvention shown in FIG. 4 they are comprised of singly coiled wiresections 18 constituting continuations of the primary coiling of themain body portion 15 of the filament 12. A slip-over wire coil 19 of asuitable refractory metal such as tungsten or molybdenum or an alloythereof is slipped over the respective filament end leg portions 17 or18. The said slip-over coil 19 is made just large enough in diameter tofit more or less snugly around the filament end leg portions 17 or 18.The filament end legs 17 or 18, together with the associated slipovercoils 19, thus form composite end conductor portions 20 for thefilament, the filament end legs serving as core members for suchcomposite conductors.

The composite end conductor portions 20 of the filament, comprised ofthe end leg sections 17 or 18 together with their associated slip-overcoils 19, are suitably connected to the respective lead-in conductors13, as by being welded directly thereto, for example. Preferably,however, they are connected to the conductors 13 in the manner disclosedand claimed in my US. Patent 2,987,643, issued June 6, 1961, andassigned to the assignee of the present invention. To this end, each endconductor portion 20 is tightly clamped against the respective lead-inconductor 13 by a thin metal strap or plate member 21 which is securelyfastened to the lead-in conductor as by welding it thereto at points oneither side of the filament end conductor portions 20, as indicated at22. The tight clamping of the coil-enclosed filament end leg 17 or 18 tothe lead-in conductor 13 thus forms a rigid mechanical clamp connectiontherebetween which constitutes the first point of completely rigidanchorage of the filament end leg outwardly therealong from the mainbody portion 16 of the filament 12. The metal strap or plate members 21may be made of any suitable material such as nickel or iron for example,and they are fastened to the lead-in conductors 13 in a manner such asto extend outwardly away from the said conductors in opposite directionstherefrom and substantially in the plane of the said conductors 13whereby the plate members 21 intercept a minimum of the radiations fromthe filament so as not to produce undesirable shadows or dark spots inthe light beam projected by the lamp. Each filament end conductorportion 20, instead of being welded directly to the lead-in conductor13, is extended outwardly beyond the lead-in conductor and is welded tothe metal strap or plate member 21 at a point along its length spacedsome distance, for example, one-eighth inch or so, outwardly thereoffrom its mechanical clamp connection to the leadin conductor asindicated at 23. The strap or plate members 21 are each formed with across corrugation 24 extending thereacross and preferably tapered downin size (i.e., both in width and depth) in a direction outwardly fromthe respective lead-in conductor 13 to provide a correspondingly taperedgroove or channel 25 for accommodating the filament end conductorportions 20 therein. This tapering of the channel or groove 25 in themetal strap 21 serves to raise or expose the filament end conductorportions 20 above the plane of the welding faces of the metal strap,thereby assuring contacting of the welding electrode with the filamentend conductor portions 20 during the welding thereof to the metal strap.

By clamping the filament end conductor portions 20 to the respectivelead-in conductors 13 by means of the metal clamping plates 21 andwelding the filament end conductor portions to the metal plates 21 atpoints out- Ward of the lead-in conductors 13 instead of directlythereto, the points of maximum flexure stress that develop in thefilament on vibration thereof then occur at the mechanical pressure orclamp connection of the filament end conductor portions 20 to thelead-in conductors and are thus kept away from the recrystallized,structurally weakened section of the filament which is produced at theweld 23 thereof to the metal strap 21. As a result, a filament joint isprovided of greatly increased vibration strength over that which isobtained where the filament is welded directly to the lead-in conductorso that the points of maximum fiexure stress in the filament are locatedat the welded and recrystallized section of the filament.

In accordance with the invention, the fiexure stresses which aredeveloped in the filament end leg sections 17 or 18 at their clampedconnections to the lead-in conductors 13 by the metal clamping plates 21are materially minimized and distributed instead more or less uniformlythroughout substantially the entire effective length of such filamentend leg sections by forming the slip-over coils 19 of progressively andsubstantially uniformly increasing stiffness, or decreasing lateralflexibility, outwardly thereof toward the respective lead-in conductor13. To such end, the wire slip-over coils 19 are, in accordance with apreferred form of the invention, wound with a varying coil pitch whichprogressively and uniformly increases, in a direction outwardly towardthe respective conductors 13, from a closely-coiled inner end section 26adjacent the coiled-coil body portion 16 of the filament 12 to a widelyopen-coiled outer end section 27 at the clamped connection of thefilament end conductor portions 20 to the lead-in conductors 13. In thisconnection, it should be noted that the lateral flexibility of a wirecoil decreases, and its resistance to lateral deformation (i.e., itsstiffness) increases in direct proportion to its coil pitch.Consequently, the use of a slip-over coil 19 having a coil pitch whichgradually increases in a direction outwardly thereof toward therespective lead-in conductor 13 provides a more or less graduallydecreasing flexibility gradient in the filament between the points wherethe filament end leg sections 17 or 18 begin at the filament proper 16and the points where they are clamped by plates 21 to the lead-inconductors 13. Thus, there is no abrupt change in the flexibilitygradient of the filament 12 toward its respective points of rigidattachment or clamping to the lead-in conductors 13, and vibrationalstresses imparted to the filament are therefore effectively distributedmore or less uniformly throughout the entire effective length of thefilament end legs 17 or 18 instead of being localized at one point alongtheir length (i.e., at their points of rigid or clamped connection tothe lead-in conductors 13) where they would then cause early rupture ofthe filament wire. The slip-over Wire coils 19 also act to dampenfilament vibration so as to reduce the amplitude thereof and therebystill further decrease the filament ruptureproducing effect of suchvibrations. The sum result, therefore, of the use of the particulargraduated coil pitch wire slip-over coil construction according to theinvention is a filament joint of greatly increased strength andresistance to vibrational stresses, as contrasted to that of prior typefilament connections employing slip-over coils of uniform coil pitchthroughout.

In the modified form of filament joint shown in FIG. 4 wherein thefilament end legs are comprised of singlycoiled wire sections 18 formedas continuations of the primary coiling of the filament proper 16, theslip-over coils 19 are in such case wound or coiled in a reversedirection to the coiled filament end legs 18. This assures that theindividual coil turns of the slip-over coils 19 will cross over theindividual wire turns of the coiled filament end legs 18 instead ofentering and becoming locked therebetween such as would otherwise occurif the two coils 18 and 19 were wound in the same instead of oppositedirections.

Although preferred embodiments of my invention have been disclosed, itwill be understood that the invention is not to be limited to thespecific construction and arrangement of parts shown, but they may bewidely modified within the spirit and scope of my invention as definedby the appended claims.

What I claim as new and desired to secure by Letters Patent of theUnited States is:

1. In an electric lamp, the combination of a lead-in conductor, and afilament having a linearly extending end leg with a wire slip-over coilsnugly fitted thereover, said end leg and slip-over coil extendingacross said lead-in conductor and being rigidly connected thereto, saidslipover coil progressively and uniformly decreasing in lateralflexibility in a direction outwardly toward said conductor.

2. In an electric lamp, the combination of a lead-in conductor, and afilament having a linearly extending end leg with a wire slip-over coilsnugly fitted thereover, said end leg and slip-over coil extendingacross said lead-in conductor and being rigidly connected thereto, saidslipover coil progressively and uniformly increasing in coil pitch in adirection outwardly toward said conductor.

3. An electric lamp as specified in claim 2 wherein the said lead-inconductor and slip-over coil are mechanically clamped to the saidlead-in conductor.

4. An electric lamp as specified in claim 2 wherein the said lead-inconductor and slip-over coil are welded to the saidlead-in conductor.

5. An electric lamp as specified in claim 2 wherein the said linearlyextending filament end leg portion is in the form of a substantiallystraight wire section.

6. An electric lamp as specified in claim 2 wherein the said linearlyextending filament end leg portion is in the form of a wire coil woundin a reverse direction to that of the said slip-over coil.

References Cited by the Examiner UNITED STATES PATENTS 2,273,762 2/ 1942Reerink et a1 313-3461 2,848,642. 8/1958 Wisco et al 313344 X 2,987,6436/1961 Ackerman 313-269 X JAMES D. KALLAM, Acting Primary Examiner.

JOHN W. HUCKERT, Examiner.

A. I. JAMES, Assistant Examiner.

1. IN AN ELECTRIC LAMP, THE COMBINATION OF A LEAD-IN CONDUCTOR, AND A FILAMENT HAVING A LINEARLY EXTENDING END LEG WITH A WIRE SLIP-OVER COIL SNUGLY FITTED THEREOVER, SAID END LEG AND SLIP-OVER COIL EXTENDING ACROSS SAID LEAD-IN 